Actinomyces viscosus ATCC 15987 was examined for the presence of cell-associated levan by absorption of myeloma proteins with antilevan activity and direct immunofluorescence. Levan was not detectable on the surface of glucose-grown A. viscosus, but after a brief incubation of these cells with 5% sucrose, they were encapsulated with tenaciously adhering levan. The levan layer constituted between 0.02 and 0.03% of the cell dry weight. In contrast, sucrose-grown A. viscosus cells possessed a low level of cell-associated levan, which was only moderately increased by incubation in sucrose and which partially existed as a loose slime rather than a tenacious capsule.
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